Method and device for determining a misalignement of the radiation characteristic of a sensor for ajusting the speed and distance of a motor

ABSTRACT

The invention relates to a device and a method used to monitor mis-adjustments of the distance sensor of a motor vehicle, combining two individual methods. Both individual methods are selected in such a way that one method has advantages in areas where the other method functions at a disadvantage, whereby the shortcomings of one method can be compensated by the strengths of the other. By combining said methods, it is possible to decide with a far greater degree of reliability whether a mis-adjustment has occurred, requiring suitable follow-up measures or whether an extreme misadjustment has occurred, requiring the shut-down of the system.

BACKGROUND INFORMATION

[0001] The present invention describes a method and a device for detecting and/or correcting misalignment of a distance sensor on a vehicle. Some methods and devices for recognizing misalignment have been known for a long time, even having the function of being able to self-correct their sensor viewing zone.

[0002] Thus, DE 197 46 524 Al describes a compensation device for compensating for the installation tolerances of a distance sensor in a vehicle. This is done by having the evaluation electronics registering the object distances and the object angles of the detected objects. These data are averaged over a specifiably long time, and the thus ascertained object angle average is accepted as the new nominal directional angle of the preceding vehicle. Furthermore, a correcting angle is calculated from the difference of the nominal directional angle and the actual directional angle. The registered object angles are corrected with this difference angle.

[0003] European Patent EP 0 782 008 A2 describes a device for calculating and correcting the deviation of the center axis of an obstacle recognition device on a vehicle and equipment for proximity-controlled cruise control based on a preceding vehicle. This system recognizes standing objects, and from the positional displacement of the standing object relative to the sensor in time, it calculates whether the standing object has a relative speed component which is orthogonal to the axis of symmetry of the sensor's viewing zone, also called the optical axis. In the case of an accurately adjusted sensor, a mean value generation in time of this lateral relative speed gives a value tending to zero. In the case of a sensor's viewing zone that is out of alignment, a value not equal to zero is obtained by the mean value generation in time, which, by its magnitude permits drawing a conclusion on the misalignment angle of the sensor. Using this method, a misalignment of the sensor can be recognized, and the sensor's misalignment can be corrected.

[0004] Both methods have a device and a method, respectively, for recognizing misalignment, and both methods correct, upon recognizing misalignment, in such a way that a correcting angle ascertained from the measured values is added to the measured object angle. Thereby the axis of symmetry of the sensor is tilted by calculation in such a way that-it approximately coincides with the central axis of the vehicle.

Description of the Present Invention, Object, Solution and Advantages

[0005] It is common to all the known methods and devices for recognizing misalignment of distance sensors that in specified travel situations they yield good results, and in other travel situations they yield results whose errors cannot be neglected. Thus, advantageous and disadvantageous travel states exist for each system.

[0006] Now, it is the subject matter of the present invention to let two or more differently defined individual procedures for misalignment recognition proceed simultaneously in combination and monitor the travel state or operate a device which makes use of two or more individual procedures. Expediently, these two individual procedures are developed in such a way that at least one procedure yields reliable values in each travel state. Thereby, the weakness of one procedure, namely that it yields unreliable values in this travel state, is compensated for by the strength of another method, since the latter yields reliable values in this travel state. For the evaluation of the results of the individual procedures, a quality factor is developed from the currently present travel state for each individual procedure, which are used for the weighting of the results of the individual procedures. A linked misalignment value can be determined, depending on the weighted results of the individual procedures as well as the results of the value linkage, which is corrected as a function of these values, or as a result of which the system is switched off for safety reasons. Defects in the sensor hardware become apparent from error images which can be represented by special misalignment vectors. Such a misalignment vector is made up of a linear combination of the misalignment values of the individual procedures. By monitoring-the up-to-date misalignment vectors, some hardware functions of the sensor important to the operation can thus be monitored. This present invention is suitable for horizontal and also for vertical misalignment recognition and/or misalignment correction. In case a vertical misalignment recognition and/or correction is also to be carried out, the sensor must also be in a position to measure the elevation angle of reflecting objects.

[0007] If a travel situation occurs in which an individual procedure used yields unreliable measured values, the results of this procedure are weighted more lightly at this point in time than another individual procedure which is expected to yield more reliable values in this travel situation, with the aid of a quality factor. By such a combination of individual procedures it is possible to compensate for the weak points of one procedure by the strength of another procedure. It is also possible to predict with greater probability, from a measured sensor misalignment, that there is indeed misalignment. If both procedures determine that there is misalignment, but in different angular directions, this can be caused by too great single errors of the procedures. However, if misalignment values appear in the same angular direction and at approximately equal angles from the vehicle's center axis, one may assume with greater probability than when only one individual procedure is used, that the sensor's axis has indeed been shifted. In this case, one can make a reliable correction or switch off the system at very much smaller misalignment values than is possible using a individual procedure. On account of this present invention, operation of a proximity-controlled vehicle under cruise control is much safer than operating a vehicle having a sensor which is monitored by only one individual procedure for misalignment. Furthermore, the error due to disadvantageous surroundings is held much smaller than with an individual procedure, since at the time of measuring, the more reliable procedure is treated as more dominant because of the lower weighting of the unreliable result.

DESCRIPTION OF THE DRAWINGS AND AN EXEMPLARY EMBODIMENT

[0008] In the following, a method and a device of the exemplary embodiment are explained in greater detail.

[0009]FIG. 1 shows a top view of two vehicles traveling one behind the other in the same lane, the following vehicle being provided with a device according to the present invention.

[0010]FIG. 2 shows a diagram which sketches the shutoff range of the system as a function of the two orthogonal individual procedures.

[0011]FIG. 3 shows a block diagram of an exemplary embodiment according to the present invention.

[0012]FIG. 4 shows an additional block diagram of a second exemplary embodiment according to the present invention.

[0013]FIG. 1 shows a lane 1, on which two vehicles 2 and 3 are traveling one behind the other, such that vehicle 3 follows vehicle 2. Vehicle 3 is equipped with a sensor 4 for speed control and proximity-controlled cruise control, which includes the subject matter of the present invention. Ray 8 represents the center axis of vehicle 3, which, in the case of an accurately adjusted sensor is identical with the axis of symmetry of the sensor's viewing zone 7. This is also the principal beam direction of the sensor's radiation characteristic. Rays 6 and 10 represent the right and left edges, respectively, of the sector-shaped sensor viewing zone, ray 8 being exactly the bisector of the two rays 6 and 10. The lines marking an accurately adjusted sensor region (6, 8, 10) were represented in FIG. 1-by solid lines. In the case of a horizontally misaligned sensor, i.e. the misalignment of the radiation characteristic was ascertained as being not equal to zero, the sensor's viewing zone is shown by broken lines 5, 7 and 9. These rays differ from rays 6, 8 and 10 only in that they are rotated by the horizontal misalignment angle theta, as in FIG. 1. In this regard, ray 5 represents the right edge of the sensor's viewing zone and ray 9 represents the left edge of the sensor's viewing zone. Ray 7 marks the bisector between rays 5 and 9, and thus the center axis of the sector-shaped viewing zone of the sensor. Angle theta 11 states by what rotation the sensor is misaligned. Expediently, this angle is measured between the motor vehicle's center axis and the axis of symmetry of the sensor's viewing zone. Inside the viewing zone of the sensor, an electromagnetic wave is emitted, preferably a radar or LIDAR signal. Objects present in this viewing zone of the sensor scatter back a reflected wave which is detected at the sensor with the corresponding propagation delay. The angle at which a reflected signal is radiated and received is designated as the object angle, and is processed further as object angle value. All objects within the sensor's viewing zone are known by object distance and object angle. From these objects a target object is selected for this, expediently that object being selected which is closest in distance and most possibly stays close to the vicinity of the longitudinal axis of the vehicle.

[0014]FIG. 2 shows a two-dimensional diagram which sketches the switch-off range as well as the functional range. The two coordinate axes 12 and 13 form an orthogonal system. Here the instantaneous misalignment value of one of the two individual procedures is plotted on each axis, whereby the misalignment value combination of the instantaneous individual misalignment values can be represented by a point in two-dimensional error space. In this exemplary embodiment the normalized error of the long-term filtering of the target object's course displacement is plotted on coordinate axis 12. The normalization occurs here in such a way that the maximum tolerable error d—alpha—obj—max of this method is marked by point 14. Analogously, the normalized misalignment value of the regression analysis of trajectories is plotted on coordinate axis 13. Normalization takes place here again in the same manner, so that the maximum tolerable misalignment value of this method, d—alpha—traj-max is marked by point 15.. Now, if both methods for misalignment recognition are evaluated separately from each other, this yields a rectangle whose center corresponds to the coordinate's origin. If the instantaneous misalignment point then lies inside this rectangle, this means that both single errors simultaneously lie below each of their limiting values, so that one may assume that the misalignment values come about through non-optimal travel situations, and the sensor's viewing zone can be readjusted. Now one can combine both methods with each other. If both methods indicate errors having the same sign, this means that the error points lie in quadrants I or III, and if possibly they also lie near straight line 16, then both methods detect approximately the same misalignment value, and, with greater probability than with the use of one individual procedure, one may assume actual determination of the radiation characteristic compared to the vehicle's longitudinal axis. Because of this, in these area, that is, in the I. and III. quadrants one can limit the functional region by removing a part of the functional region. This region, which now belongs to the switching off region, is thus called “broadened switching off region”.

[0015] It should be noted that the borders between functional region and switching off region 17, as well as between functional region and broadened switching off region 18, as well as between switching off region and broadened switching off region 19 were illustrated in all four quadrants in FIG. 2 as straight lines, for simplicity's sake, but in practice they could be shaped as any desired curves.

[0016] Likewise, one may introduce further “broadened switching off regions”, so as to be able to model the border of the functional region or the functional regions, as the case may be, as desired.

[0017] The functional manner of this combination method is indicated in FIG. 3. The two single procedures “long-term filtering of the target object's travel-path misalignment” 20 as well as “regression analysis of trajectories ” 21 calculate in each case an instantaneous misalignment value d—alpha—obj or d—alpha—traj, as the case may be. These two values are passed on to function blocks 24, 25 and 26, as in FIG. 3.

[0018] The travel situation is simultaneously ascertained from measured travel dynamics of other systems and/or additional vehicle data. In this connection, it is determined whether the vehicle is traveling straight ahead or along a curve, whether it is going upwards or downwards, or whether further conditions impairing the measuring procedures are fulfilled, expediently in that a yaw rate signal, a pitch signal or additional signals describing travel dynamics are used. From the ascertained travel situation, a quality factor is calculated for each procedure in function block 22. The quality factor for the long-term filtering of the target object travel path displacement is passed on as q—obj, and the quality factor for the regression analysis of trajectories is passed on as q—traj. These quality factors are passed on to blocks 24, 25 and 26 in such a way that block 25 receives both quality factors q—obj and q-traj, block 24 only q—obj and block 26 only q—traj. In block 25 the broadened switching off region is now formed using the function.

F 1(d—alpha—obj, q—obj, d—alpha—traj, q—traj)>. . . K 1(d—alpha—obj—max, alpha traj—max)

[0019] the two misalignment values d-alpha—obj and d-alpha—traj being weighted with the aid of quality, factors q—obj and q—traj. If this equation is satisfied, then a greater error is present than is permissible, and a switching off request is passed on to block 27.

[0020] In block 24, using single misalignment value d—alpha—obj and the respective quality factor q—obj, a test is made whether

F 1(d—alpha—obj, q—obj)>q—alpha—obj—max

[0021] is satisfied. If yes, the error is greater than is permissible, and the switching off request is passed on to block 27. In block 26, using single misalignment value d—alpha—traj and the respective quality factor q—traj, a test is made whether the condition

F 2(d—alpha—traj, q—traj)>q—alpha-traj-max

[0022] is satisfied. If yes, the error is greater than is permissible, and the switching off request is passed on to block 27. If block 27 receives at least one switching off request from one of blocks 24, 25 or 26, it is passed on to block 29 that the proximity-control system and the cruise control shall be switched off.

[0023] In FIG. 4 a further exemplary embodiment of the present invention is illustrated. This includes all the parts described in FIG. 3, but was additionally supplemented. Thus block 24 has been newly added. Block 23 receives the two single misalignment values d—alpha-obj and d-alpha—traj as well as the pertaining quality factors q obj and q—traj. In block 23 a linked misalignment value d alpha—comb is formed from these values, using the single misalignment values. The value thus created, d—alpha—comb is then passed on to likewise newly added block 28 where correction of the main radiation direction of the radiation characteristic is performed. If function block 28 is informed of a request to switch off, it causes deactivation of the correction and also deactivates the entire proximity-control system and cruise control system.

[0024] The values d-alpha—obj—max as well as d—alpha-traj—max can be constant values, but they can also be functions shown in FIG. 2 as arbitrary straight lines, or they could look like arbitrarily shaped curves.

[0025] A plurality of variants are conceivable during system deactivation. Thus switching off the vehicle control can be expediently kept up only so long as misalignment values lie in a correctable region, that is, that block 27 receives at least one switching off request, or it can be switched off until the vehicle is started the next time and a negative self-diagnosis has been carried out, or again, deactivation is kept up until this error message, which is stored in a nonvolatile memory, is reset in a garage.

[0026] The correction of the sensor's viewing zone can also be made in a different way. One possibility is to add the determined linked misalignment angle value to all measured angle values, so that the new sensor viewing zone is tilted by calculation into the correct position. Another possibility provides for displacing the edge of the sensor's viewing zone, which lies on the side in whose direction the axis of symmetry of the viewing zone has been displaced toward the center until the axis of symmetry of the sensor's viewing zone is identical to the vehicle's center axis. This would have the disadvantage that the sensor's viewing zone becomes less at each correction, and after some operating period no longer exists.

[0027] In addition to monitoring the sensor adjustment, one can also monitor the sensor hardware. With certain combinations of the single misalignment values (d—alpha—obj; d—alpha—traj) one may conclude, on account of experiences gathered, that there are special defects in the sensor's hardware. If these combinations arise, the regulating system must be switched off on account of possible hardware defects.

[0028] By linking a plurality of procedures, it is possible on the one hand to determine with greater probability that the ascertained correction value corresponds to the actual sensor malposition than when using a single procedure, whereby a robust monitoring procedure is ensured, and furthermore it is also possible to monitor parts of the sensor hardware for their functioning. 

What is claimed is:
 1. A method for ascertaining an alignment error of the radiation characteristic of a sensor for a cruise control and a proximity-control system of a vehicle with respect to the vehicle longitudinal axis (8), wherein at least two differently defined single procedures (20, 21) are used for ascertaining the alignment error, in that the misalignment values of the single procedures (d—alpha—obj, d—alpha—traj) are linked with each other to form a linked misalignment value and the proximity-control and cruise control system is switched off when a value formed from the single misalignment values and-the quality factors is greater in quantity than an associated, predefinable limiting value, or one of the misalignment values of the single procedures, which was weighted by the associated quality factor, is greater than an associated, predefinable limiting value.
 2. The method as recited in claim 1, wherein the instantaneously present travel state is recorded and is drawn upon (22) for ascertaining the linked misalignment value d—alpha—comb, particularly by weighting the misalignment values of the single procedures using quality factors (q—traj, q—obj), which are formed from the instantaneous travel state.
 3. The method as recited in claim 1, wherein one of the single procedures is designed in such a way that a misalignment value (d—alpha—obj) is ascertained (20) on the basis of a mean value generation in time via the instantaneous target object angle to the vehicle's center axis, and another of the single procedures is designed in such a way that a further misalignment value (d—alpha—traj) is ascertained (21) using a trajectories method, in which the relative change in the object position of recognized, preferably standing backscattering objects, with the aid of the vehicle's own speed, is used for ascertaining the lateral relative speed of the object with respect to the vehicle's center axis.
 4. The method as recited in claim 1, wherein the radiation characteristic of the sensor with respect to the vehicle's longitudinal axis is continuously corrected by the linked misalignment value (d—alpha—comb).
 5. The method as recited in claim 1, wherein the cruise control and proximity control system is deactivated when one of the limiting values is exceeded, and reactivation of the system is prevented until such time as the misalignment values of the single procedures and the linked misalignment value lie within a permissible error region, or reactivation is prevented until such time as the ignition of the vehicle is switched on again and a self-diagnosis without findings has been carried out, or the system stores this deactivation state in a non-volatile manner, and reactivation of the system is prevented until such time as the deactivation state stored in a non-volatile manner is canceled.
 6. The method as recited in claim 1, wherein the main propagation direction of the radiation characteristic is continuously corrected by tilting the radiation characteristic by the addition of the linked misalignment value (d—alpha—comb) to the measured object angle values, so that the main propagation direction of the beam coincides with the vehicle's longitudinal axis, or by displacing the lateral boundary of the sector-shaped radiation characteristic (5), in whose direction the main propagation direction of the beam (7) is displaced from the vehicle's longitudinal axis (8), towards the center until such time as the sensor's viewing zone has been narrowed down to such an extent that it is symmetrical with respect to the vehicle's longitudinal axis (8).
 7. The method as recited in claim 1, wherein, given certain combinations of misalignment values of the single procedures or of quality factors, special defects in the sensor hardware can be inferred.
 8. A device-for ascertaining an alignment-error of the radiation characteristic of a sensor for cruise control and proximity control of a vehicle with respect to the vehicle's longitudinal axis (8), wherein at least two differently defined single procedures (20, 21) are used for ascertaining the alignment error, by linking (23) the misalignment values of the single procedures (d—alpha—obj, d—alpha—traj) together to form a linked misalignment value (d—alpha—comb), as a function of which the proximity-control and cruise control system can be switched off.
 9. The device as recited in claim 8, wherein device means are provided which record the instantaneously present travel state and form therefrom the quality factors (q—traj, q—obj), which are drawn upon (22) for ascertaining the linked misalignment value, particularly by weighting the misalignment values of the single procedures using these quality factors. 